The aim of the proposed work is to obtain experimental evidence that bears on three topics: (1) the features that characterize the segments of language, (2) the surface form that segments take when they are concatenated into larger units, and (3) models of the processing by which concatenation occurs. In addition to the experimental studies, we will develop theories and models that attempt to account for the influence of characteristics of the human perception, production and cognition systems on all three of these areas. Research concerned with topic (1) will involve collecting data on the production, acoustic form and perception of various classes of speech sounds, together with experimental studies and modelling of some basic properties of the human sound-generating and auditory perception systems. Research directed toward topic (2) will include studies of the types of phonetic variation that occur in various languages, particularly English, and how this variation interacts with linguistic factors and with biomechanical factors and principles of speech motor control. Research on the speech planning process (topic 3) includes studies of coarticulation planning, and determination of acoustic-phonetic rules and their ordering in fluent speech. Other experiments will examine speech errors (using an error-elicitation paradigm) and explore segment-manipulating abilities of speakers (involving "play-languages" like Pig Latin). Results will be interpreted in terms of models for speech planning.